1. Field of the Invention
The present invention relates to an airbag and an airbag device for occupant at passenger's seat, which are included in an instrument panel of a vehicle, for example.
2. Description of the Related Art
Conventionally, an airbag device for occupant at passenger's seat is employed for protecting an occupant at passenger's seat of a vehicle. This airbag device is included in an instrument panel which is opposed to the occupant at the passenger's seat, and is provided with constituent elements such as: a case member substantially shaped like a case; an airbag substantially shaped like a bag, which is retracted and accommodated in this case member; an inflator which is mounted on the case member, for supplying gas to the airbag; and a cover member for covering the retracted airbag. In addition, in a state in which a control unit detects collision of a vehicle, this airbag device allows the inflator to be activated to supply gas inside of the airbag; and the cover member to be pushed and opened to inflate and expand the airbag forward of the occupant having taken the passenger's seat, thereby protecting the occupant while mitigating the shock delivered thereto.
As to such airbag device, a variety of constructions are proposed allowing the device to appropriately protect the occupant, even in a so called OOP state in which the airbag inflates and expands with the occupant being close to the airbag device; and for example, a construction employing an output variable type inflator is known (refer to Japanese Laid-open Patent Application No. 11-321506, for example). Further, in this construction, an outer bag and an inner bag are provided to duplex the airbag, and a portion at which the outer bag is folded and a portion at which the inner bag is folded are sewn and jointed with each other by means of a severable tear seam. In this construction, in a case where the inflator is activated at a low output, the tear seam is not severed, and the airbag slightly inflates. Alternatively, in a case where the inflator is activated at a large output, the tear seam is severed, and the airbag significantly inflates, allowing expansion characteristics of the airbag to vary depending upon the occupant, attempting to improve performance of protecting the occupant.
However, in the construction of Japanese Laid-open Patent Application No. 11-321506, the output variable type inflator is required, and the portions at which the outer and inner bags are folded respectively are needed to be sewn and jointed with each other. Therefore, a manufacturing process becomes complicated, and reduction of manufacturing cost is not easy.
In addition, as to such airbag device, there is known a construction in which: ground cloths constituting the airbag are sewn and jointed with each other at a breakable jointing portion; vent holes formed on the ground cloths are covered with a vent hole cover; ends of the vent hole cover are jointed with the ground cloths at the jointing portion; and a separation portion, which is expandable or breakable if a predetermined load or more is applied, is provided on the vent hole cover (refer to Japanese Laid-open Patent Application No. 2006-224748, for example).
However, in the construction of Japanese Laid-open Patent Application No. 2006-224748 as well, there is a need to include a vent hole cover on which a separation portion, which is expandable or breakable if a predetermined load or more is applied, is provided; a structure becomes complicated; and reduction of manufacturing cost is not easy.